Experts, please help out a newbie

[Victor Kang]

I have a few questions. It might be silly and relatively easy to answer. Bare with me as I am super new to this. 

I found a 4plex in Las Vegas for $225,000. Im thinking of paying 50% down which equals $112,500. With a 30 year fix at 6% interest rate equals $830/month = $9,960/year = $298,800/30 years. With my initial $112,500 down payment and the total mortgage at $298,800 = $411,300. This sounds like an awful investment as I am paying almost double. Does this math makes sense or am I off? I know this can be a really dumb question but as I have mentioned, I am really new. Please experts, enlighten me. Any feedback will help tremendously.

Thank you!

[Franco Li]

Why are you deciding to put 50% down? Keep in mind that I don't know the area, but you can theoretically buy two houses at 25% down at a similar price - assuming the rental rates make sense...